FiloCell™ cellulose filaments are produced at Kruger's Trois-Rivières mill

It's been over three years since the strategic alliance was formed between FPInnovations and Kruger Biomaterials Inc. to develop the process technology and commercial applications of cellulose filaments (CF), initially conceived at FPInnovations' Pointe Claire, QC laboratories. The business model of this alliance allows Kruger to gain a lead in CF manufacturing, while FPInnovations members have access to CF from the Kruger Biomaterials plant for applications development.

In the interim, a lot of progress has been made. The CF pre-commercial plant in Trois-Rivières, QC was designed and built on a fast-track schedule, in less than 7 months. High quality CF was produced within 2 months of start-up, and production was ramped up to the designed 5 t/d capacity in 9 months. That capacity makes it the largest cellulosic biomaterial plant in the world. However, that 5 t/d capacity is for one shift per day only, so there is ample room for more production – up to 6,000 t/a for 24 h/7 day operation. FPInnovations' intellectual property portfolio has been strengthened and expanded with patents on the process granted in 6 countries, several patents filed on new CF applications, and additional applications in the pipeline.

The FiloCell™ product is aimed at paper strength reinforcing, new grade development and lightweighting applications, and new groundbreaking uses in composite materials, concrete mixes and many diverse applications. The fastest progress in field-testing and application development has been in the Canadian paper industry where 30 on-machine trials have been concluded so far, some of them covering several weeks of machine production time. Strength enhancement in paper is a natural application for CF since it has a very good fiber to fibril bonding potential made possible by a high aspect (length to width) ratio, which is achieved by gently peeling fibrils from kraft pulp fibers while still maintaining the length. That results in a paper sheet which has stronger wet and dry strength for the same basis weight.

Improved or unique paper properties

Balázs Tolnai, General Manager Technology at Kruger's Industrial Product Division, emphasizes the value of CF in a paper furnish: "CF provides extraordinary strength which allows significant furnish optimization and reduced chemical dosages. It also permits the development of new products."

Regarding the paper machine trials, Tolnai continues, "The majority of the trials were focused on developing new grades with improved and/or unique properties or to produce grades that had been out of the capabilities of the paper machine. Some machines have never been able to run low basis weight because of the wet web strength and poor runnability. Now, with CF, the wet web strength is improved as well as the dry strength. With the help of CF we are able to produce high strength, light weight products and we are also able to translate the strength coming from the CF to other properties (like opacity) by adjusting the machine operation and furnish composition. During the trials the machine operators have become accustomed to the different drainage profiles and machine draws required for CF-enhanced grades." Trial runs have been on paper machines using both mechanical pulp and mixtures of mechanical and chemical pulp. Wood-free grade trials are being planned.

He continues, "CF quality can be adjusted to match end user needs. We have full flexibility, but it is a trade-off between achieving certain quality parameters and paper machine productivity. The quality is checked online every fifteen minutes by an analyzer developed by FPInnovations.

An online analyzer developed by FPInnovations measures CF tensile strength so it can be closely controlled.

Press breaks one third with CF

CF has also proved its value in printing plants using trial rolls of CF-enhanced publication papers. Tolnai explains, "CF not only can improve strength of the paper, but also improves its uniformity by eliminating low and high points and tightening the distribution of the sheet strength. Since we are able to eliminate the low spots in the sheet, the paper performs better in the pressroom. A LWC grade paper with CF had one third of the breaks than paper with no CF at the same strength."

Trials in a press room show that break frequency has been reduced by two-thirds with CF-enhanced paper. This is because sheet strength is more uniform as shown in the histogram chart.

Good dispersion of CF is required to untangle the filaments. The mill trials have used several types of commercial pulpers with success. A mobile platform designed by FPInnovations is also available. To date, CF has been shipped in bulk bags at 30% solids. A 100% dry CF film was produced in a pilot machine trial at InnoFibre in Trois-Rivières. This dry film form avoids extra shipping costs for full time commercial applications. The film is fully dispersible with standard papermaking equipment.

CF is currently shipped at 30% solids in bulk bags. A dispersible 100% dry sheet has been produced on InnoFibre's pilot paper machine in Trois-Rivières

New applications require collaboration

Papermaking is a natural application for cellulose filaments, however there are a multitude of potential applications in other industries. Composite materials and concrete mixes are enticing and encouraging so far. This type of research and development will take more time and collaboration with universities and other development partners. Tolnai says, "The universities and research centres together with relevant and dedicated industrial players are a must for the development of CF applications. Even though they are at the laboratory scale some significant discoveries have been made already, including high strength high performance concretes, technology to produce dry and dispersed CF, and lightweight CF-containing plastic composites."

Kruger Biomaterials, in collaboration with UQTR, (Université de Québec à Trois-Rivières) has developed a surface treatment which allows for the production of dried CF which is "fluffy" and dispersible. That is a key requirement for composites. The water uptake of the CF containing composites drops to extremely low levels.

Concrete strength improved

"We have been working with the University of Sherbrooke on developing CF- containing high performance concretes. We are looking at specialty applications, not commodity. The main benefit is improved rheology and strength properties with minimal CF addition. In certain grades with 0.1% CF addition we can improve the concrete strength by 1 or 2 orders of magnitude," he explains. Since the concrete mix with CF is thixotropic, its viscosity decreases with shear forces, thus making it more fluid. This produces a more homogeneous concrete with less phase separation before the concrete is set. With lower viscosity the pumping costs to the top of high skyscrapers are lower.

Flexural strength of cement paste has been improved remarkably by small amounts of CF.

Breakthroughs coming?Over the next year or two what could be the imminent breakthroughs that would make CF a fully commercial product? Tolnai responds, "First, the commercialization of specialty paper products. Within the next year we hope to have a 24/7 application on a paper machine. That would be a success. Then our expectations are for development of light weight composites and high performance concrete."

"The current CF plant with 24/7 operation will be able to supply the market needs for a couple of years," he explains. A production-scale plant of 100 t/d is in line with Kruger's projections of a market of 150,000 t/y for the papermaking applications and a similar size market for other applications.